The present invention relates to a semiconductor wafer having an identification indication and a method of manufacturing a semiconductor wafer having an identification indication.
Conventionally, an individual identification indication such as numerals and bar codes is applied to each semiconductor wafer before forming a semiconductor circuit on the semiconductor wafer so as to identify each semiconductor wafer. The indication is provided by engraving the front surface or the rear surface of the semiconductor wafer, in general, by means of laser beam radiation. However, various treatment processes are applied to the semiconductor wafer thereafter in order to form a semiconductor circuit in each chip area. After the treatment processes, the identification indication disappears or becomes unclear so that the recognition of the identification indication becomes difficult.
FIGS. 14 and 15 show a conventional semiconductor wafer 104 with a chip pattern 102 and an identification indication 16 formed on the surface of the semiconductor wafer 104. The identification indication 16 is formed by engraving the wafer 104 by laser beam radiation. A layer film (single layer or multi-layer) such as an insulating film 106 is formed on the semiconductor wafer surface having the identification indication 16. FIG. 14 is a diagram showing the surface of the semiconductor wafer 104 with engraving, that is, the identification indication 16 formed thereon by the laser beam radiation. FIG. 15 is an enlarged cross-sectional view of a part of the engraved portion, that is, the identification indication 16 portion on the semiconductor wafer surface of FIG. 14. As shown in the cross-sectional view of FIG. 15, the wafer 104 is engraved by the laser beam substantially vertically with respect to the surface with a clear outline so that the indication can be read accurately before forming the insulating film 106. However, if the insulating film 106 is formed on the semiconductor wafer surface, it is difficult to accurately reflect the outline of the engraved portion on the semiconductor wafer surface to the surface of the insulating film 106 so that the outline reflected on the insulating film 106 surface becomes unclear with dull corners. Therefore, it is difficult to read the indication accurately after forming the thin film. That is, if the insulating film 106 is formed by the CVD technology, the outline of the groove portion is ruined so that the outline of the insulating film 106 becomes a smooth mountain-like shape as shown in the cross-sectional view of FIG. 15. Also, the outline of the engraving formed on the substrate surface becomes unclear, and thus accurate reading becomes difficult.
FIG. 16 shows the state where the surface of the insulating film 106 is applied with the CMP treatment, and further, a metal film 108 of, for example, Al is formed thereon in the cross-sectional structure of FIG. 14. In this case, since the surface of the insulating film 106 is flattened by the CMP treatment, the surface of the metal film formed on the insulating film 106 can be flat as well. Therefore, when the CMP treatment is applied, the outline of the identification indication 16, that is, the engraved portion disappears on the metal film so that the identification indication 16 cannot be read out.
FIG. 17 shows the semiconductor wafer surface with a chip pattern 102 formed on the entirety thereof so as to minimize the loading effect of the RIE treatment and/or the CMP treatment. By forming the chip pattern on the entirety of the semiconductor wafer surface, the outline of the engraving of the identification indication 16 formed on the semiconductor wafer surface before forming the chip pattern becomes unclear as the semiconductor circuit formation treatment process proceeds on the wafer surface so that the accurate reading of the identification indication 16 becomes difficult.
FIG. 18 is a plan view of the semiconductor wafer surface with the engraving formed thereon. FIG. 19 is an enlarged cross-sectional view of a part of the engraved portion. If the engraving is formed on the surface of the semiconductor wafer 104 by the laser beam radiation, actually not only the groove but also a bump (uplift) 202 is formed in the engraved portion as shown in FIG. 19. Due to the bump 202, the homogeneity of the flatness is deteriorated in the subsequent CMP treatment. That is, since an abrading pad (not illustrated) of an abrading device cannot or hardly makes contact with the rear part of the semiconductor wafer 104 at the time of contacting and abrading the bump 202 of the engraved portion due to the height of the bump 202, an under polish is generated on the semiconductor wafer surface portion in the vicinity of the bump 202. Furthermore, when attaching such a wafer with a bump on a stage in a stepper, the bump portion of the wafer rises so that the light beam cannot be focused well in the lithography.
FIG. 20 is a side view of the semiconductor wafer 104 where the identification indication 16 is formed by engraving the rear surface of the semiconductor wafer 104 by the laser beam radiation. The rear surface of the semiconductor is, however, applied with the wrapping treatment (backside grinding) preceding the packaging, and thus by the wrapping treatment, the wafer 104 (such as a silicon substrate) usually having about 725 um thickness becomes thinner to about 300 um thickness. By the wrapping treatment, the identification indication 16 by engraving is completely eliminated without remaining until the cutting and separating process of the wafer 104 into chips.
As heretofore mentioned, in the case the identification indication 16 is formed on the surface of the wafer, the outline of the engraving on the semiconductor wafer surface disappears or becomes unclear by the subsequent processes on the wafer surface for forming a semiconductor circuit so that it becomes difficult to read the identification indication 16. On the other hand, in the case the identification indication 16 is formed on the rear side of the wafer, the identification indication 16 by engraving completely disappears by the wrapping treatment of the wafer rear surface preceding the packaging and thus it is impossible to read the identification indication 16.